The purpose of the present study was to determine whether the administration of 2.5 ppm F in the drinking water of rats would confer lifelong protection against dental caries. It was observed that no differences occurred in the caries scores of animals fed fluoride and controls after either 2 weeks or 4 weeks. Animals usually develop pit and fissure caries only during this time. However, significant differences were observed in animals fed fluoride for 8, 12 and 16 weeks.